1. Field of the Invention
The present disclosure generally relates to methods of conditioning (i.e., “shaking down”) a shape memory alloy wire for predictable use as an actuator; and more particularly, to an improved apparatus, method and model for conditioning shape memory alloy wires.
2. Discussion of Prior Art
Shape memory alloy is used increasingly in place of traditional actuators because of their compactness, high work density, low cost, ruggedness, high force generation, and relatively large strains. One well known concern in the art associated with SMA wires, however, is degradation in performance as actuation cycles accumulate. Significant reductions have been observed as soon as only tens or hundreds of cycles. Thus, to insure stable long-term performance, manufacturers typically recommend very conservative limits on the suggested maximum operational force, ensuring minimal losses in actuator stroke at the cost of reduced overall performance and efficiency. For example, it is appreciated that the maximum load for one class of 15 mil, 70° C. wire is specified at 20 N, which is low considering that actuation motion for the wire can still be obtained for loads above 80 N.
It is also known in the art to shake down shape memory alloy wire prior to use as an actuator by running the specimen through a plurality of thermally induced activation cycles until the recovered strain stabilizes. Concernedly, however, conventional shakedowns typically present one-size-fits-all protocols that do not take into consideration many aspects of the proposed application. As such, wire performance and/or fatigue life is often inefficiently and unnecessarily reduced.